Usually, a wind turbine facility comprises a tower, which carries a nacelle with the wind turbine and a generator. A converter of the wind turbine facility is usually positioned inside the tower, for example directly on or shortly above a basement, on which the tower is erected.
The converter usually comprises a grid side converter and a generator side converter, which are coupled by a DC link. This DC link usually is interconnected with a voltage limiting unit, which stabilizes and balances the DC link during disturbances or low voltage ride throughs. The voltage limiting unit comprises a resistor, which may be electrically connected to the DC link for converting electrical energy from the DC link irreversibly to thermal energy (i.e. heat) which may be radiated to the environment.
During a low voltage ride through (in which the voltage in a grid supplied by the wind turbine facility decreases) it is usually not possible to feed all the energy from the generator to the grid. On the other hand, during a low voltage ride through, a torque reference for the generator may not be substantially changed to avoid torque jumps which may lead to gearbox damages and heavy oscillations. These two requirements may result in a voltage limiting unit with huge thermal capacity to absorb the full power from the generator for a couple of seconds. During this, the resistor of the voltage limiting unit may heat up to several hundred degrees Celsius.
US 2012/0133342 A1 describes a liquid resistor filled with seawater for a voltage limiting unit.
DE 102009054374 A1 describes to reuse the thermal energy from a voltage limiting unit by using a temperature difference between voltage limiting unit and the environment to create a supply voltage with a thermal element for a cooling fan.
WO 2013/135504 A1 relates to controlling a wind turbine, when the grid is no available. A heating device is mentioned, which is provided by chopper resistors of a converter. The generated heat may be used for heating a lower part of a tower of the wind turbine. A control board for controlling the chopper resistors is mentioned.
EP 2 270 331 A2 relates to power management of a wind turbine during grid faults. It is described, how surplus power may be dissipated with a resistive element connected to a DC link of the converter of the wind turbine.